Create osx_build_script_toxcore.txt

OS X shell script to do everything from git pull to sudo make install for toxcore, after dependencies have already been installed, by MacPorts, from source, etc.
Update INSTALL.md

Added MacPorts related info. to Section heading "OS X Non-homebrew"
Update INSTALL.md
Made toxdns header cpp-friendly
Merge branch 'lyubod-master'
Merge branch 'toxdns-header-fix' of https://github.com/nurupo/InsertProjectNameHere
fix #1104
Merge branch 'master' of https://github.com/dubslow/toxcore